SYMPTOMS OF DISEASE. 191 



colours, frequently commencing at the margins 

 of leaves, are characteristic symptoms of the 

 injurious action of acid gases in the air. 



Brown and blackish spots on Pears are caused 

 by a species of TJirips. 



In many cases the minute spots of Rust-fungi 

 on one and the same leaf are bright orange yellow 

 (uredo), deep brown, or almost purple-black 

 (teleutospores), foxy-red brown (older uredospores), 

 or dead slaty black where the old teleutospores 

 have died off e.g. Uroniyces Fabae on Beans, 

 U. Pisi on Peas, etc. 



Parti-coloured leaves. The leaves sometimes 

 start shrivelling with red edges, while yellow, red, 

 and finally brown and black blotches appear on 

 the lamina, from no known cause e.g. Vines. 

 In other cases similar mimicry of the autumnal 

 colouring of leaves results from the action of acid 

 gases. 



Burning is a common name for all cases where 

 the leaves turn red or red-brown in hot, dry 

 weather, and many varieties are distinguished in 

 different countries and on different plants, because 

 species react dissimilarly. The primary cause is 

 usually want of water drought. 



Foxy leaves are a common sign of drought on 

 hot soils, and the disease may usually be recognised 

 by the gradual extension of the drying and fox-red 

 colour proceeding from the older to the younger 

 leaves, and from base to apex e.g. Hops. 



Coppery leaves. The leaves of the Hop, etc., may 

 show yellow spots and gradually turn red-brown 



